High Temperature Erosion Performance of Nanostructured and Conventional TiAlN Coatings on AISI-304...

TECHNICAL PAPER TP 2814

High Temperature Erosion Performance of Nanostructuredand Conventional TiAlN Coatings on AISI-304 Boiler SteelSubstrate

Jasmaninder Singh Grewal • Buta Singh Sidhu •

Satya Prakash

Received: 23 August 2013 / Accepted: 8 April 2014

� The Indian Institute of Metals - IIM 2014

Abstract According to modern design philosophy better

overall performance can be obtained with the modification

of the surface structure and their properties without dam-

aging underlying bulk material or substrate. The surface

engineering can be classified in two broad classes: surface

modification and surface coating. In the present research

TiAlN coating was deposited on AISI-304 grade boiler

steel using three different techniques, out of which two

were thin nano coatings deposited at different temperatures

of 500 and 200 �C developed by Oerlikon Balzers rapid

coating system machine under a reactive nitrogen atmo-

sphere. One conventional coating of TiAlN was deposited

by plasma spraying method. The coated samples were

characterized relative to their coating thickness, microh-

ardness, porosity and micro structure. The optical micros-

copy, the X-ray diffraction analysis and field emission

scanning electron microscope (FESEM with EDAX

attachment) analysis have been used to identify various

phases formed after coating deposition on the surface of

AISI-304 grade boiler steel. The erosion studies were

conducted on uncoated as well as coated specimens in

simulated coal fired boiler environment using an air jet

erosion test rig at various impingement angles of 30�, 60�and 90�. The alumina particles of average size of 50 lm

were used as erodent at a velocity of 35 m/s. The eroded

samples were analysed with SEM/EDAX and optical pro-

filometer. The main objective of this research work was to

increase the life of boiler tubes by using nanostructured and

conventional TiAlN coatings and at the same time to

compare the performance of coatings with respect to bare

AISI-304 grade boiler steel. The nanostructured TiAlN

coatings has shown minimum erosion rate as compared to

conventional TiAlN coating and uncoated AISI-304 grade

boiler steel. Maximum erosion was observed at an angle of

30� as compared to 60� and 90� indicative ductile

behaviour.

Keywords Solid particle erosion �Nanostructured coatings � Physical vapour deposition

1 Introduction

Solid particle erosion is the progressive loss of original

material from a solid surface due to mechanical interaction

between that surface and solid particles. Erosion is a seri-

ous problem in many engineering systems, including steam

and jet turbines, pipelines and valves used in slurry trans-

portation of matter and fluidized bed combustion systems

[1–3]. Gas and steam turbines operate in environments

where the ingestion of solid particles is inevitable. In

industrial applications and power generation systems such

as coal burning boilers, fluidized beds and gas turbines,

solid particles are produced during the combustion of

heavy oils, synthetic fuels and pulverized coal. Moreover,

the shape of the particles and angle of impingement plays

an important role in the erosion of materials [4–7].

It is now a generally accepted practice to apply coatings

to the components in fossil fuel energy generation

J. S. Grewal (&)

Department of Production Engineering, Guru Nanak Dev

Engineering College, Ludhiana, India

e-mail: [email protected]

B. S. Sidhu

PTU, Kapurthala, India

S. Prakash

Department of Metallurgical and Materials Engineering,

IIT Roorkee, Roorkee, India

123

Trans Indian Inst Met

DOI 10.1007/s12666-014-0413-8

processes to provide thermal insulation, erosion and wear

resistance and in chemical process plants or boilers to

protect the surface of structural steels against surface

degradation processes such as wear, corrosion and erosion

[8, 9]. However, thermal spraying is an effective and low

cost method to apply thick coatings to change surface

properties of the component [10]. For more than four

decades plasma spraying has been used to deposit a wide

range of metals, ceramics and even composite materials for

many different applications [11]. Bulk nanostructured

materials (in general referring to a grain size smaller than

100 nm) have exhibited outstanding mechanical properties

such as exceptional hardness, yield strength and wear

resistance [12, 13].

Plasma assisted physical vapour deposition processes

(PAPVD) allow the deposition of metals, alloys, ceramic

and polymer thin films onto a wide range of substrate

materials. Nanostructured materials indeed behave differ-

ently than their microscopic counterparts because their

characteristic sizes are smaller than the characteristic

length scales of physical phenomenon occurring in bulk

materials [14–16].

In this work nanostructured and conventional titanium

aluminium nitride coatings were deposited on AISI-304

grade boiler steel substrate. The emphasis has been put on

the influence of nanostructured TiAlN coatings in com-

parison with conventional TiAlN coatings on the erosion

behaviour of Fe-based AISI-304 grade boiler steel. Nitride

based coatings deposited on AISI-304 stainless steels,

reduce the total wear rate by half with respect to (wrt) bare

stainless steel [17].

2 Experimental Details

2.1 Selection of Substrate Material

AISI-304 grade boiler steel has been selected as substrate

after consultation with Guru Nanak Dev Thermal Plant

Bathinda (India). The nominal composition of the material

is compared with the actual composition analysed by using

Brammer Standard 84-E stainless steel with Atomic

Emission Spectrometer (AES-DV4) at Research and

Development Centre for Bicycle and Sewing Machine at

Ludhiana, India as shown in Table 1.

Specimens of approximate dimensions of 20 mm 9

15 mm 9 5 mm were cut from the substrate sheet and then

polished with emery papers of 220, 400, 600 grit sizes,

subsequently on 1/0, 2/0, 3/0 and 4/0 grades and finally

mirror polished using cloth polishing wheel machine with

1 lm lavigated alumina powder suspension.

2.2 Development of Coatings

A front loading Balzers rapid coating system (RCS)

machine was used for the deposition of nanostructured thin

coatings by PAPVD process at Oerlikon Balzers Coating

India Ltd., Gurgaon, India. Two coatings namely Balinit

Futura Nano i.e. thin nano TiAlN coating at 500 �C tem-

perature with composition of Ti-50 % and Al-50 % in the

atmosphere of nitrogen and Balinit Futura Nano Arctic i.e.

thin nano TiAlN coating at 200 �C temperature with again

the same composition of Ti-50 % and Al-50 % in the

atmosphere of nitrogen were deposited on the substrate. A

conventional thick coating TiAl was deposited by plasma

spraying technique at Anod Plasma Spray Ltd., Kanpur,

India. The nitriding of which was done in the laboratory at

IIT Roorkee. The summary of the coating deposition

parameters of both nano and conventional is given below in

Tables 2 and 3. The cross sectional image of as coated

nanostructured TiAlN coating deposited at 500 and at

200 �C and conventional TiAlN coatings deposited on

AISI-304 grade boiler steel are shown in Fig. 1.

2.3 Erosion Studies in Simulated Coal Fired Boiler

Environment

The erosion studies were carried out using a high temper-

ature air-jet erosion test rig (Fig. 2). The erosion test

conditions utilized in the present study are listed in

Table 4. The impact velocity of 35 m/s has been selected

as per the ASTM G7607 standard under clause 9.1.4. A

standard test procedure was employed for each erosion test.

The uncoated as well as the coated specimens were pol-

ished down to 1 lm alumina wheel cloth polishing to

obtain similar condition on all the samples before being

subjected to erosion run. The samples were cleaned in

acetone, dried, weighed to an accuracy of 1 9 10-5 g

using an electronic balance, eroded in the test rig for 3 h

and then weighed again to determine weight loss. In the

present study irregular shaped alumina (Al2O3) of 50 lm

size was used as erodent. The scanning electron micro-

scope (SEM)/EDAX of alumina (Al2O3) is shown in Fig. 3.

Erosion rates in terms of volumetric loss (mm3/g) for

Table 1 Chemical composition (wt%) of AISI-304 grade boiler steel

Elements C Mn Si Cr Ni P S Other elements Fe

Nominal 0.08 2.00 1.00 18.0–20.0 8.0–10.5 0.045 0.03 – Balance

Actual 0.07 1.14 0.33 18.46 8.12 0.028 0.012 – Balance


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different uncoated and coated alloys were compared. The

eroded samples were analyzed with SEM/EDAX and

optical profilometer. The erosion rate data for each coated

alloy has been plotted along with uncoated alloy in order to

assess the coating performance. Efforts have been made to

understand the mechanism of erosion.

3 Results and Discussion

3.1 Coating Microstructure and Properties

The typical microstructure of PAPVD coatings of nano-

structured TiAlN deposited at 500 and 200 �C has been

shown in Fig. 4a, b, has a dense and nano-layered structure,

identical to the results of Yang et al. [18, 19]. All the

TiAlN coatings with different Al concentrations showed

small finest grains as reported by Yang et al. [18] and a

dense structure with a strong (111) texture of CrTiAlN

coating is reported by Yang et al. [19].

The mechanical properties of plasma and D-gun sprayed

coatings are anisotropic because of splat structure and

directional solidification as reported by Hocking [20]

which corroborates the results of plasma sprayed, post

nitrided conventional TiAlN coating (Fig. 4c) of the pres-

ent investigation which indicate the coating is homoge-

nous, massive and free from cracks. D-gun spray process is

a thermal coating process which gives good adhesive

strength, low porosity and coating surface with compres-

sive residual stresses. Hearley et al. [21] also reported

Fig. 1 Cross sectional image of as coated a nano-structured TiAlN

coating deposited at 500 �C, b nano-structured TiAlN coating

deposited at 200 �C and c conventional TiAlN coating deposited on

AISI-304 grade boiler steel

Table 2 Summary of nano coating deposition parameters

Machine used Standard Balzers rapid coating system

(RCS) machine

Make Oerlikon Balzers, Swiss

Targets composition For TiAlN coating: Ti, Ti50Al50

Number of targets Ti(02), Ti50Al50 (04)

Targets power (kW) 3.5

Reactive gas Nitrogen

Nitrogen deposition

pressure (Pa)

3.5

Substrate bias voltage (V) -170 to -40

Substrate temperature

(�C)

450 ± 10

Coating thickness (lm) 4 ± 1

Table 3 Summary of conventional coating deposition parameters

Arc current (A) 750

Arc voltage (V) 45

Powder feed rate (rev/min) 5.2

Spraying distance (mm) 90–110

Plasma arc gas (argon) pressure (psi) 58

Powder gas pressure (psi) 60

AUX gas pressure (psi) 10


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identical results of distinctive splats or lamellae associated

with thermal spray process, in case of HVOF sprayed NiAl

intermetallic coating with good homogeneity and

uniformity.

Hardness is the most frequently quoted mechanical

property of the coatings. The microhardness of the con-

ventional thick TiAlN coating was found to be in the range

of 900–950 Hv which is almost identical to the findings of

Adachi and Nakata [22], Chen and Hutchings [23], Vuor-

isto et al. [24] and Westergard et al. [25]. The hardening of

the conventional TiAlN coating observed in the current

study might have occurred due to high speed impact of the

coating particles during plasma deposition similar to the

findings of Sidhu et al. [26] and Hidalgo et al. [27].

The bond strength of the conventional TiAlN coating

was measured on three specimens as per ASTM standard

C633-01. This test method covers the determination of the

degree of adhesion (bonding strength) of a coating to a

substrate or the cohesion strength of the coating in a ten-

sion normal to the surface. The test consists of coating one

face of a substrate fixture, bonding this coating to the face

of a loading fixture, and subjecting this assembly of coating

and fixtures to a tensile load normal to the plane of the

coating. A data acquisition system has continuously

recorded the tensile load exerted by the machine. It is

adapted particularly for testing coatings applied by thermal

spray, which is defined to include the combustion flame,

plasma arc, two wire arc, high-velocity oxygen fuel and

detonation processes for spraying feedstock, which may be

in the form of, wire, rod or powder. Average bond strength

Fig. 2 Experimental set-up for erosion–corrosion in simulated coal-fired boiler environment a air jet erosion tester and b interior view of

specimen loading chamber

Table 4 Erosion test conditions

Erodent material Alumina (irregular shape)

Erodent specifications 50 lm Al2O3

Particle velocity (m/s) 35

Erodent feed rate (g/min) 2

Impact angle (�) 30, 90

Test temperature Sample temperature 400 �C and air

temperature 900 �C

Nozzle diameter (mm) 4

Nozzle to sample distance (mm) 10

Test time (h) 3


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Fig. 3 Analysis of alumina (Al2O3), a FESEM morphology and b EDAX compositional analysis

Fig. 4 Optical micrograph (9200) of the surface of as coated AISI-304 grade boiler steel a nanostructured TiAlN coating at 500 �C,

b nanostructured TiAlN coating at 200 �C and c conventional TiAlN coating


123

of 68.77 MPa was observed which is almost in agreement

with the results reported by Adachi and Nakata [22].

The grain size of nanostructured thin coatings was

estimated from Scherrer’s formula i.e. D = 0.9k/B cosh,

where B is the corrected full width at half maximum of

Bragg’s peak, k is X-ray wavelength and h is the Bragg’s

angle. The calculated grain size for nanostructured TiAlN

coating deposited at 500 and 200 �C was found to be 15

and 14 nm, respectively, which are nearly equal to the

values of nanostructured TiAlN coatings reported by Yang

et al. [19], Pei et al. [28], Yoo et al. [29], Falub et al. [30]

and Man et al. [31].

The porosity analysis is having prime importance in

high temperature erosion studies. The dense coatings are

supposed to provide good resistance as compared to

porous coating. The porosity measurements were made

with PMP3 inverted metallurgical microscope with ste-

reographic imaging. The porosity of as sprayed nano-

structured TiAlN coatings deposited at 500 and 200 �C

is lower than or nearly equal to the porosity values

reported by Chawla et al. [14], Braic et al. [32], Grzesik

et al. [33] and Alberdi et al. [34] for TiAlN nanocom-

posite coatings. The porosity of as sprayed conventional

TiAlN coating after gas nitriding was less than 0.6 %

which is in accordance with the results reported by

Lackner et al. [35], Ohnuma et al. [36] and Leyendecker

et al. [37].

The microstructural and mechanical properties of

nanostructured thin TiAlN coatings deposited at 500 and

200 �C are given in Table 5 and of the conventional TiAlN

thick coating are given in Table 6.

3.2 Erosion Rate Wrt Impingement Angle

Impingement angle is one of the most important parameters

for the characterizing the erosion behaviour of materials. In

general different materials exhibit different response to the

impingement angle. The macrographs for uncoated and

coated AISI-304 grade boiler steel subjected to erosion studies

in simulated coal fired boiler environment are shown in Fig. 5.

The volume erosion rate of the samples is given in Table 7.

The shape of the scar (developed by constant strike of

erodent) is circular in case of normal impact at 90�, semi-

elliptical at 60� and elliptical in case of oblique impact of

30� of the erodent. The uncoated AISI-304 grade boiler steel

has shown the thin scale. The erosion seems to clean off the

scale of the surface in the eroded region. The impact of

erodent removes the scale down to the substrates–scale

interface. Away from this eroded region a thin layer of scale

was observed on the surface and the eroded region showed

rust coloured discolouration and the scar was surrounded by

dark rust coloured thin ring further surrounded by brown

ring. The nanostructured TiAlN coated AISI-304 grade

boiler steel has shown clear marks of erosion. The colour of

the coated specimen has been changed from violet grey to

whitish around the scar and further surrounded by blackish

blue ring. The colour of the scars was observed as dark grey

surrounded by whitish grey colour ring. In the case of

conventional thick TiAlN coating the formation of dark grey

coloured scar surrounded a white coloured thin ring, further

surrounded by light brownish black ring was observed.

For erosion damage, there are two dominant mecha-

nisms i.e. the ductile type damage, through cutting and

Table 5 Microstructural and mechanical properties of nanostructured thin TiAlN coatings at 500 and 200 �C on AISI-304 grade boiler steel

Coatings Surface

roughness

(nm)

Particle size (nm) Porosity

(% age)

Coating

thickness

(lm)

Micro hardness

(Hv 0.05)

Elastic modulus,

E (GPa)

Coating

colorsScherrer formula

Nanostructured TiAlN

coating at 500 �C

3.70 15 \0.5 5.9 3,300 343 Violet–grey

Nanostructured TiAlN

coating at 200 �C

3.65 14 \0.5 6.0 3,300 375 Light violet–grey

Table 6 Microstructural and mechanical properties of conventional thick TiAlN coating on AISI-304 grade boiler steel

Coating Surface roughness

(lm)

Coating thickness

(lm)

Porosity (% age) Bond strength

(MPa)

Micro hardness

(Hv)

Coating

colorsAs

sprayed

After gas

nitriding

Conventional TiAlN

coating

10.35–15.45 174 2.30–4.25 \0.6 68.77 900–950 Grey


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brittle type damage by cracking. Impact angle is defined as

the angle between the target material and the trajectory of

the erodent. Dependence of erosion rate on the impact

Fig. 5 Surface macrograph of

uncoated and coated AISI-304

grade boiler steel exposed to

high temperature erosion studies

in stimulated coal fired boiler

environment

Table 7 Volume erosion rate (10-3 9 mm3/g) at different impact angles

Impact

angles (�)

Uncoated AISI-304 grade

boiler steel

Nanostructured TiAlN coating

deposited at 500 �C

Nanostructured TiAlN coating

deposited at 200 �C

Conventional TiAlN

coating

90 0.2783 0.03741 0.03659 1.8217

60 0.3428 0.04343 0.04132 1.9837

30 0.499 0.05608 0.05439 2.103

Fig. 6 Impact angle influence on erosion rate in case of ductile and

brittle materials (Sundararajan et al. [48])

Fig. 7 Influence of impingement angle on erosion rate of nanostruc-

tured TiAlN coatings deposited at 500 and 200 �C and conventional

TiAlN coating


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angle is largely determined by nature of the target mate-

rials. There is a dramatic difference between ductile and

brittle materials when the weight loss in erosion is mea-

sured as a function of impact angle as reported by Bhushan

and Gupta [38]. Brittle erosion deals with the material

removal due to crack formation whereas ductile erosion

occurs due to exclusion of microplatelets of the base

material from craters which then flattened and fractured.

The erosion rate of ductile materials (like metals and

alloys) is maximum at intermediate impact angles (15�,

30�) as shown in Fig. 6 whereas the maximum erosion rate

of brittle materials (like glass) is usually obtained at normal

impact angle i.e. 90�. This occurs because ductile materials

are capable of absorbing the large amount of energy pro-

duced by the impacting particles without fracture and

brittle materials are capable of withstanding large amount

of shear stress. In general ductile material fail in shear

before tension and brittle materials fail in tension before

shear. For semibrittle materials such as transition metal

nitrides, cutting is the major erosion mechanism at a low

impingement angle, while cracking plays a more significant

role in erosion damage process at a high impingement

angle. The erosion rate wrt impact angle of uncoated AISI-

304 grade boiler steel, nanostructured TiAlN coating

deposited at 500 and 200 �C and conventional TiAlN

coating has been shown in Fig. 7 indicated that maximum

erosion took place at 30� which indicate ductile behaviour

as proposed by Murthy et al. [39]. The authors Finnie et al.

[40–42], Shimizu and Noguchi [43], Oka et al. [44],

Wellman and Allen [45] recognized the basis of erosion

mechanism that maximum erosion occurs at shallow angle

of 20–30� for ductile materials and brittle materials reaches

higher erosion rates at higher angles of 80–90� which

corroborates the results of present research. Most of the

metallic materials irrespective of temperature exhibit a

ductile behaviour i.e. a maximum erosion rate at oblique

impact angles reported by Tabakoff and Vittal [46].

However, Hutchings [47] and Sundararajan and Roy [48]

reported the angular dependence of erosion is not a char-

acteristic of material alone but also depends upon the

conditions of erosion and hence suggests that the terms

brittle and ductile in the context of erosion should therefore

be used with caution. This leads to the further detailed

microscopic analysis.

Basically the erosion rate of the coatings was obtained

by dividing the weight loss per gram of erodent with the

coating density [19]. The erosion rate of nanostructured

TiAlN coatings due to continuous impact of erodent par-

ticles i.e. aluminium oxide of 50 lm size at 30� impact

angle is minimum as compared to conventional TiAlN

coating and bare AISI-304 boiler steel. The results of dif-

ferent impact angles i.e. 30�, 60� and 90� considered in the

present study are almost identical to the observations made

by Yang et al. [18, 19], which reported ductile behavior at

30� impact angle and poor erosion resistance.

In erosion testing the material is eroded by continuous

impact of eroded particles, the erosion starts at the centre

first then proceeds towards the edges of the samples as

exactly happened in the present investigation, similar to the

Fig. 8 Column chart showing

the volume wear rate of

uncoated and coated AISI-304

grade boiler steel eroded at

impact angles of 30�, 60� and

90�

Fig. 9 Surface scale morphology and EDAX patterns on different

locations on eroded uncoated and coated AISI-304 grade boiler steel

exposed to high temperature erosion in simulated coal fired boiler

environment at impingement angle of 30�, a uncoated AISI-304 grade

boiler steel, b nanostructured TiAlN coating deposited at 500 �C,

c nanostructured TiAlN coating deposited at 200 �C and d Conven-

tional TiAlN coating

c


123


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findings reported by Mann and Arya [49], Stack et al. [50,

51]. The steady state erosion rate column chart (Fig. 8) has

shown that nanostructured TiAlN coatings are weakly

dependent upon the angle of impingement and has a small

difference in erosion rate at 30�, 60� and 90� impact angles

whereas in case of conventional TiAlN coating erosion rate

is quiet substantial. This is in the complete agreement with

the study of Tabakoff and Vittal [46]. Hearley et al. [21]

have shown similar behavior for NiCr coatings.

The impact velocity is one of the key parameters and

can be regulated by varying the air pressure. The impact

velocity of 35 m/s selected for the present study in accor-

dance with ASTM G7607 standard under clause 9.1.4 is

almost similar to the impact velocities selected by Mishra

et al. [52] i.e. 40 ± 3 m/s for coated cobalt based alloys for

boiler steels.

3.3 Morphology and Erosion Mechanism

The mechanism by which material is removed from coating

under erosive conditions may be either ductile or brittle.

Microstructural characteristics enhancing erosion resis-

tance include high compactness, low porosity, fine grain

size, good adhesion and absence of cracks [53–55]. From

Fig. 4 it is clear that higher erosion resistance of PAPVD

sprayed nanostructured coatings are closely correlated with

their fine structure, high compactness and low porosity in

addition to their favourable compositions. In contrast

conventional TiAlN coating exhibited the highest erosion

wastage among the coatings tested which was attributed to

its large splat size, high porosity and fine cracks network.

Figure 9 has shown the typical morphologies of the

surfaces of the uncoated AISI-304 grade boiler steel,

nanostructured TiAlN coating deposited at 500 and 200 �C

and conventional coating of TiAlN eroded at high tem-

perature of 900 �C with erodent aluminium oxide at an

angle of impingement of 30�. The erodent impingements

produced rougher elliptical surface at the centre area of the

erosion scar with deeper erodent cutting marks which

corresponds to a higher erosion rate. At glancing

impingement, erosion is dominated by cutting with no

coating removal through cracking in case of nanostructured

coatings of TiAlN. Due to its high hardness, the TiAlN

coating exhibits high resistance to the coating removal

through cutting. The identical findings are given by Yang

et al. [18, 19] i.e. in case of CrTiAlN coatings at low

impingement angles of 15� and 30�. Sidhu et al. [56] and

Bellman and Levy [57] also reported identical results as

solid particle erosion rate of substrate steels is maximum at

30� impact angle. The material subjected to erosion ini-

tially undergoes plastic deformation and is later removed

by subsequent impacts of the erodent on the surface. Due to

cutting by erodent particle, lips and ridges are formed at the

bank of the grooves which are fractured or removed from

the grooves with further erosion.

It is well known that the mechanism of high temperature

erosion always involves first the oxidation of the surface

and then the removal of the oxide pieces and this process is

effected by the oxidation rate of the material and the

adherence between the oxide layer and the substrate [27].

Alloys that are developed for heat and oxidation resistance

typically form a protective layer of chromia or alumina.

The more rapidly this layer is established, the better pro-

tection is offered [26]. However in case of conventional

TiAlN coating the sample surfaces at high temperature i.e.

900 �C were more irregular and showed small pieces of the

coating were chipped off. At this temperature the oxidation

of the coating has affected its erosion behavior and the

erosion of the oxide layer seems to be the main weight loss

mechanism.

It is clear from Fig. 9d that there are some radial and

lateral cracks as well as loosened pieces of the eroded

specimen surfaces. Cracking is thought to form first at splat

boundary during impact of particles. Under continual

impacting of particles the radial and lateral cracks are

developed. Finally small voids and pits are formed. On the

other hand the uncoated AISI-304 grade boiler steel

showed finer and smoother morphology (Fig. 9a) which

corresponds to its lower erosion wastage as compared to

conventional TiAlN coating. However the eroded surface

having some evidence of deformation indicated by small

craters, striations and indentations. Similar findings are

given by Wang and Verstak [58].

Figures 10 and 11 has shown the morphology of the

surfaces at 60� and 90�, respectively. The erosion is again

ductile in nature at both the impact angles, the coating

being hard and with uniform homogeneity, the results of

the present investigation are identical to the findings of

Hearley et al. [21] for erosion rate as a function of impact

angle for NiAl intermetallic coatings produced by thermal

spraying.

At impingement of angles higher than 30� the eroded

nanostructured TiAlN coatings surface has also shown

cutting marks produced by eroded particles whereas in case

of conventional TiAlN coating it appears to have local

valleys where the coating has experienced more material

removal through cracking as compared to nanocoatings of

TiAlN. Even more valleys were observed at 90� than 60�.





boiler steel, b nanostructured TiAlN coating deposited at 500 �C,

c nanostructured TiAlN coating deposited at 200 �C and d conven-

tional TiAlN coating

c


123


123


123

The SEM examination revealed that TiAlN coating

behaves like a semiductile material which experiences

solid particle erosion damage involving both cutting and

cracking.

The lower erosion rate of nanostructured TiAlN coatings

implies that these coatings have a higher resistance to

cracking at 90� or in other words a higher toughness and

also should be attributed to their favourable microstructure

with more uniform distribution of smaller TiAl particles,

lower porosity and oxidation rates. These findings are

identical to the observations made by Yang et al. [19] and

Wang and Shui [59].

3.4 Effect of Porosity

The porosity content of the nanostructured coatings of

TiAlN has been measured less than 0.5 %, due to which

dense structured coatings gave good erosion resistance,

whereas conventional coating after nitriding was having

porosity value less than 0.6 %, which is in agreement with

Sidhu et al. [26], as the nitriding of TiAl has increased the

density of the coatings and this made the structure dense.

Hearley et al. [21] reported that coating porosity is often

located along the lamella boundaries. Not only it will

influence the strength of the inter lamella bonding but may

also initiate micro cracking leading to loss of lamellae and

thus removing the coating. Similar results are reported in

case of conventional TiAlN coating of the present inves-

tigation, thus indicating that nanostructured TiAlN coatings

are having better porosity performance than conventional

TiAlN coating wrt erosion rate.

4 Conclusions

(1) The conventional thick TiAlN coating (by plasma

spraying followed by gas nitriding process) and the

nanostructured thin coatings of TiAlN at temperatures

of 500 and 200 �C were successfully deposited on

AISI-304 boiler steel.

(2) During solid particle erosion test both the nanostruc-

tured TiAlN coatings performed better than the

conventional TiAlN coating and uncoated AISI-304

boiler steel at all the three impingement angles of 30�,

60� and 90�.

(3) Nanostructured TiAlN coatings show fine, dense,

uniform and nanolayered microstructure, whereas

conventional TiAlN coating showed homogenous,

massive structure and free from cracks.

(4) No evidence of macro or micro cracking was

observed in the nanostructured TiAlN coatings,

however conventional TiAlN coating showed some

micro cracks after erosion.

(5) Ductile behaviour is indicated in case of uncoated

AISI-304 boiler steel and nanostructured TiAlN

coatings whereas conventional TiAlN coating showed

semiductile behavior.

References

1. Kosel T H, Lubrication and Wear Technology. ASM Handbook,

Vol. 18, ASM International, Materials Park (1992), p 199.

2. Zhang Y, Cheng Y B S, and Lathabai S, Wear 240 (2000) 40.

3. Wood R J K, Mater Des 20 (1999) 179.

4. Getu H, Spelt J K, and Papini M, Wear 292–293 (2012) 159.

5. Shimizu K, Xinba Y, and Araya S, Wear 271 (2011) 1357.

6. Wang X, Fang M, Zhag L, Ding H, Liu Y, and Yang J, Mater

Chem Phys 139 (2013) 765.

7. Laguna-Camacho J R, Marquina-Charvez A, Mandez-Mandez J

V, Vite-Torres M, and Gallardo-Hernandez E A, Wear 301(2013) 398.

8. Wang B Q, Geng G Q, and Levy A V, Surf Coat Technol 54–55(1992) 529.

9. Ramesh M R, Prakash S, Nath S K Sapra P K, and Vanktaraman

B, Wear 269 (2010) 197.

10. Turunen E, Varis T, Gustafsson T E, Keskinen J, Falt T, and

Hannula S-P, Surf Coat Technol 200 (2006), 4987.

11. Ding C, Chen H, Liu X, and Zeng Y, in Thermal Spray 2003.

Advancing the Science and Applying the Technology, (eds) Mo-

reau C, and Marple B, ASM International, Materials Park (2003),

p 455.

12. Leblanc L, in Thermal Spray 2003. Advancing the Science and

Applying the Technology, (eds) Moreau C, and Marple B, ASM

International, Materials Park (2003), p 291.

13. Luo H, Goberman D, Shaw L, and Gell M, Mater Sci Eng A 346(2003) 237.

14. Chawla V, Sidhu B S, Puri D, and Prakash S, J Aust Ceram Soc

44 (2008) 56.

15. Fedrizzi L, Rossi S, Cristel R, and Bonora P L, Electrochimica

Acta 49 (2004) 2803.

16. Chawla V, Puri D, Prakash S, Chawla A, and Sidhu B S, J Miner

Mater Charact Eng 8 (2009) 715.

17. Alegria-Ortega J A, Ocampo-Carmona L M, Suarez-Bustamante

F A, and Olaya-Florez J J, Wear 290–291 (2012) 149.

18. Yang Q, Seo D Y, Zhao L R, and Zeng X T, Surf Coat Technol

188–189 (2004) 168.

19. Yang Q, Zhao L R, Cai F, Yang S, and Teer D G, Surf Coat

Technol 202 (2008) 3886.

20. Hocking M G, Surf Coat Technol 62 (1993) 460.

21. Hearley J A, Little J A, and Sturgeon A J, Wear 233–235 (1999)

328.

22. Adachi S, and Nakata K, Surf Coat Technol 201 (2007) 5617.

23. Chen H, and Hutchings I M, Surf Coat Technol 107 (1998) 106.

24. Vuoristo P, Niemi K, Makela A, and Mantyla T, in Proc 7th

National Thermal Spray Conference, Boston, Massachusetts

(1994), p 121.





boiler steel, b nanostructured TiAlN coating at 500 �C, c nanostruc-

tured TiAlN coating at 200 �C and d conventional TiAlN coating

b


123

25. Westergard R, Erickson L C, Axen N, Hawthorne H M, and

Hogmark S, Tribol Int 31 (1998) 271.

26. Sidhu B S, Puri D, and Prakash S, Mater Sci Eng A368 (2004)

149.

27. Hidalgo V H, Varela J B, Menendez A C, and Martinez S P, Wear

247 (2001) 214.

28. Pei Y T, Galvan D, De Hosson J Th M, and Cavaleiro A, Surf

Coat Technol 198 (2005) 44.

29. Yoo Y H, Le D P, Kim J G, Kim S K, and Vinh P V, Thin Solid

Films 516 (2008) 3544.

30. Falub C V, Karimi A, Ante M, and Kalss W, Surf Coat Technol

201 (2007) 5891.

31. Man B Y, Guzman L, Miotello A, and Adami M, Surf Coat

Technol 180–181 (2004) 9.

32. Braic M, Balaceanu M, Braic V, Vladescu A, Pavelescu G, and

Albulescu M, Surf Coat Technol 200 (2005)1014.

33. Grzesik W, Zalisz Z, Krol S, and Nielslony P, Wear 261 (2006)

1191.

34. Alberdi A, Marin M, Diaz B, Sanchez O, and Galindo R, Vacuum

81 (2007) 1453.

35. Lackner J M, Waldhauser W, Ebner R, Keckes J, and Schoberl T,

Surf Coat Technol 177–178 (2004) 447.

36. Ohnuma H, Nihira N, Mitsuo A, Toyoda K, Kubota K, and Ai-

ziwa T, Surf Coat Technol 177–178 (2004) 623.

37. Leyendecker T, Lemmer O, Esser S, and Ebberink J, Surf Coat

Technol 48 (1991) 175.

38. Bhushan, B, and Gupta B K, Handbook of Tribology: Material

Coatings and Surface Treatments, McGraw-Hill, New York

(1991).

39. Murthy J K N, Rao D S, and Venkataraman B, Wear 249 (2001)

592.

40. Finnie I, Wear 3 (1960) 87.

41. Finnie I, Wolak J, and Kabil Y, J Mater 2 (1967) 682.

42. Finnie I, Wear 19 (1972) 81.

43. Shimizu K, and Noguchi T, Wear 176 (1994) 255.

44. Oka Y I, Ohnogi H, Hosohawa T, and Matsumura M, Wear

203–204 (1997) 573.

45. Wellman R G, and Allen C, Wear 186–187 (1995) 117.

46. Tabakoff W, and Vittal B V R, Wear 86 (1983) 89.47. Hutchings I M, Tribology: Friction and Wear of Engineering

Materials, Metallurgy and Material Science Series, Edward

Arnold Publications, London (1992).

48. Sundararajan T, and Roy M, Tribol Int 30 (1997) 339.

49. Mann B S, and Arya V, Wear 249 (2001) 354.

50. Stack M M, Stott F H, and Wood G C, Wear 162–164 (1993) 706.

51. Stack M M, Purandare Y, and Hovsepian P, Surf Coat Technol

188–189 (2004) 556.

52. Mishra S B, Chandra K, Prakash S, and Venkataraman B, Surf

Coat Technol 201 (2006) 1477.

53. Raask E, Erosion Wear in Coal Utilization, Hemisphere, Wash-

ington, DC (1988).

54. Stridh B, Hedenqvist P, Olsson M, and Soderberg S, in Proc 7th

International Conference on Erosion by Liquid and Solid Impact,

Cavendish Laboratory, Cambridge (1987), paper 19.

55. Levy A V, and Wang B Q, Wear 121 (1988) 325.

56. Sidhu H S, Sidhu B S, and Prakash S, Surf Coat Technol 202(2007) 232.

57. Bellman R Jr, and Levy A, Wear 70 (1981) 1.

58. Wang B Q, and Verstak A, Wear 233–235 (1999) 342.

59. Wang B Q, and Shui Z R, Wear 253 (2002) 550.


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High Temperature Erosion Performance of Nanostructured and Conventional TiAlN Coatings on AISI-304...

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